Smoke-sweep fixes: exact saves, local dates, safer remove, readable markers

- Garden and plant dialogs keep centimeters as the source of truth
  (LengthField in lib/units.ts): a no-change Save no longer rewrites
  900 cm as 899.922 or a 45 cm spacing as 44.958, bumping versions and
  writing bogus history entries on the way.
- The UI stamps every date with the browser's local day (lib/dates.ts).
  Journal notes already did; plop placement, fill and removal now do too,
  so a 9 pm placement isn't "planted tomorrow". The fill endpoint gained an
  optional plantedAt; API and agent callers still default to UTC today.
- Removing an object that holds plants asks first and says how many go
  with it. An empty one still goes straight away (one Undo restores it).
- The expanded plant card's action row wraps instead of clipping "Delete".
- Monogram lettering switches to a dark ink on pale marker colors (garlic,
  cabbage, marigold) instead of near-white on near-white.
- Copy-as-plan proposes the next free year and warns when the typed name
  already exists, so two gardens can't both read as "the 2027 plan".
- Plan cards show the base name with a "2027 plan" tag, so the year — the
  point of the name — survives truncation.
- A rejected model spec now says which model and why: a wrapped
  ErrInvalidInput's reason reaches the client as the 400's message, and the
  Settings field shows it inline instead of toasting "invalid input".

Also defuses a clock bomb in TestRemainingReturnsWhenAPlantingIsRemoved,
which only passed while the real date was before 2026-08-01.

Co-Authored-By: Claude Fable 5 <[email protected]>

internal/service/seed_lots_test.go

@@ -99,9 +99,12 @@ func TestRemainingReturnsWhenAPlantingIsRemoved(t *testing.T) {
 	lot := seedLot(t, s, owner, plant.ID, 100, nil)
 	ctx := context.Background()
 
-	ten := 10
+	// Dated explicitly: left to default, plantedAt is the real UTC day, and the
+	// removal below has to come after it — a test that only passed before
+	// 2026-08-01 is the kind of clock bomb this avoids.
+	ten, planted := 10, "2026-07-01"
 	pl, err := s.CreatePlanting(ctx, owner, bed.ID, PlantingInput{
-		PlantID: plant.ID, XCM: 0, YCM: 0, RadiusCM: 20, Count: &ten, SeedLotID: &lot.ID,
+		PlantID: plant.ID, XCM: 0, YCM: 0, RadiusCM: 20, Count: &ten, SeedLotID: &lot.ID, PlantedAt: &planted,
 	})
 	if err != nil {
 		t.Fatalf("CreatePlanting: %v", err)